The invention relates generally to antenna systems and, more particularly, to methods for coupling energy into and out of an antenna apparatus or the like from an external transmission line structure.
Metal-to-metal junctions in electronic circuitry are known to sometimes cause the xe2x80x9cdiode junction effectxe2x80x9d which has results in a non-linear voltage-current characteristic. Radio frequency (RF) signals flowing through such a non-linear junction have been known to create inter-modulation products having frequencies that are different from the original RF signals. This frequency effect is known as passive inter-modulation (or PIM). Sometimes these passive inter-modulation products will manifest themselves as relatively strong interference signals within the underlying system that can compromise system performance. At a minimum, these products can make it more difficult to meet system specifications for spurious signal levels. Thus, junctions that are likely to generate such non-linear effects should generally be avoided.
Therefore, there is a need for circuit structures in radio frequency systems that avoid the use of metal-to-metal junctions in the RF signal flow path.
The present invention relates to a connector structure for use in transferring radio frequency (RF) energy into and/or out of an RF circuit module. The connector structure utilizes capacitive coupling to provide an RF ground connection for the module, thus avoiding metal-to-metal contact in the RF signal ground path. The connector structure also provides a direct current (DC) ground connection for use in providing a signal flow path for DC and other low frequency signal components. The connector structure is designed so that a majority of the RF signal energy flowing through the connected ground connection flows through the capacitive coupling and relatively little flows through the DC short. Thus, the probability of generating passive inter-modulation products within the metal-to-metal contacts of the DC short are significantly reduced. The connector structure is particularly beneficial in applications involving relatively high RF signal current levels, such as in transmit antennas being fed by high output power amplification circuits.